Because you got the ultra 50k badge, and only the longest distance badge is awarded for a single activity. To get a marathon badge your activity needs…
I have a similar problem - I just did a 56km ultra race (link below) and I did get a badge ULTRA 50KM but during it also run my first marathon 42km but I did not get this badge even though in my personal data you can see a record on 42km marathon. Why is this 42km badge not achevied ?
Because you got the ultra 50k badge, and only the longest distance badge is awarded for a single activity. To get a marathon badge your activity needs to be longer than 42.2 km, but shorted than 50 km.
